Risk of moisture damage from valve replacement?

[drinksfromtap]

I'm planning on replacing a valve on a steel tank (Faber HP 120). I'm concerned about the possibility of moisture from the ambient air entering the tank and potentially causing rust issues - should I be? When dive shops or VIP facilities swap out valves, do they use a procedure where they purge the tank with dry air before re-installing the valve? I live in Florida and plan to do the swap in an air-conditioned area, install the new valve immediately after removing the old one, and getting the tank filled promptly after the replacement is complete.

Thanks for any advice you can provide.

 

[Scared Silly]

Drain the tank slowly and let it become one with the room (ie. same temperature not cooler). Remove the old valve and put the new one on and yer done. Nothing to worry about.

FWIW the air in the tank is already dry air there is little mixing that goes on in the time that it takes to do a VIP. That one can always cap the tank while the valve is being worked on.

 

[drinksfromtap]

Cool - thanks.

 

[spectrum]

Cool - thanks.

No, room temperature....

 

[herman]

If possible you might want to borrow a transfill whip to add back a few psi to the tank just to keep some tank monkey from insisting it be VIPed because it's very low in pressure. Way to many believe the under 100 psi lets moisture in BS. I do suggest you keep the valve closed after you install it. While it is small, the tank will breath as it warms and cools pulling in moist air as it does, no need to allow any more moisture in than is necessary.

 

[Graeme Tolton]

The low pressure=vip rule was invented by dive shops to scare new divers into not running their tanks low. There certainly is some merit to it, but if moisture forms inside a tank, the air was bad.

To answer the op's question, its nothing to worry about if the new valve is installed soon after the old one is removed. The air inside an unpressurized tank only accounts for <.5% of the air in the tank when full @ 3000 psi.